1. Field of the Invention
The present invention relates to a catheter which is inserted into a living body, for example, a blood vessel, in order to directly measure within the living body biological data such as blood pressure, the pH of the blood and the saturation degree of oxygen in the blood.
2. Description of the Prior Art
A typical conventional catheter which is inserted into, for example, a blood vessel to measure biological data such as blood pressure, the pH of the blood and the saturation degree of oxygen in the blood has an arrangement such as that shown in FIGS. 3(a) and 3(b). More specificlly, a sensor element 1 for detecting biological data such as blood pressure, a base 3 for supporting the sensor element 1 and lead wires 5 for electrically connecting the sensor element 1 to an external measuring device (not shown) are assembled together in advance, inserted into the bore in a sheathing tube 7 which is fabricated in advance, and positioned in such a manner that the sensitive surface of the sensor element 1 faces a measuring window 9 provided in the tube 7. In this state, the gap between the tube 7 and the assembly constituted by the sensor element 1, the base 3 and the lead wires 5 is filled with a sealing resin 11, as also is the distal end portion of the tube 7, the assembly thereby being secured in position within the tube 7 and a catheter thus being completed. In some cases, a sensor protecting film 13 is provided over the measuring window 9 so as to protect the sensitive surface of the sensor element 1.
The conventional catheter suffers, however, from the following problems. Namely, since the assembly which is constituted by the sensor element 1, the base 3 and the lead wires 5 is inserted into the bore in the sheathing tube 7, the space which could be effectively utilized for mounting the assembly is narrowed by the wall thickness of the tube 7. More specifically, the effective cross-sectional area which can be used to mount the assembly is what remains after subtraction of the wall thickness of the tube 7 from the total cross-sectional area determined by the outermost diameter of the catheter, i.e. the tube, which means that the cross-sectional area of the tube 7 cannot be utilized effectively. In the above-described structure of the conventional catheter the wall thickness of the tube 7 cannot be reduced to any great extent since the greater part of the structural strength required of a catheter depends on the strength of the tube 7, and it is therefore impossible to utilize the relatively thick wall portion of the tube 7 for mounting the assembly. Accordingly, it has been difficult to cope with the need to reduce the diameter of the catheter, to assemble together a plurality of kinds of sensor elements in order to form a composite sensor means without substantially increasing the outer diameter of the catheter, or to incorporate a tube for injection of a medical fluid or for collection of blood in the above-described arrangement so as to provide a multifunctional catheter without substantially increasing the outer diameter of the catheter.